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Old 11-23-2021, 05:19 PM   #1
MarkEHansen
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Wires too short to remove my Dometic furnace

We have a 2019 Cougar Half Ton 26RBSWE and need to pull the Dometic furnace. It started giving us trouble yesterday and today won't light at all.


The fan will come on and run, but there is no clicking from the igniter. Earlier, we could turn it off for about 2 minutes and try again and it would work, but now, we've tried turning it off for several minutes and even pulling the 12V fuse for a few minutes, but it just won't light.


We think it must be the controller board or the sail switch. I would like to pull the furnace out so I can see both, but can't get there. The access is under the fridge on the inside of the camper. I've removed the air return grill and then did the following:
1. Removed the heat ducts;
2. Removed the gas line
3. Removed the two mounting screws on the bottom/front of the case.


The unit will move out toward the inside of the camper, but will only go so far before the wiring is pulled tight. I can only get the front of the case about 1 inch outside of the opening. Not nearly far enough to get at the back of the unit.


The wires don't have any type of connection block/plug that I can see. They go straight from inside the top of the furnace case up into the outside cavity for the fridge.


How do I pull this thing out? Any help would be greatly appreciated.
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Old 11-23-2021, 05:39 PM   #2
chuckster57
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There are 4 wires:

Red-power
Black- ground
2 blue- thermostat.

You can cut the wires, make note of the blue ones, it shouldnít matter but I use tape on both sides to match them back up. If needed you can splice in extensions.
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Old 11-23-2021, 05:59 PM   #3
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Thanks Chuckster. I was afraid you were going to say that. I can reach the wires to cut them, but I would never be able to reconnect them.

I guess I would have to get some comparable wire and a soldering iron/solder so I can extend them before reassembly? I don't have those with me.

I tried banging on the outside edge of the furnace case, hoping to dislodge any debris fouling the sail switch, but no luck there either.

I'll try the wire-cutting once I get home in a couple days.

What about disconnecting the wires from within the fridge cavity and letting them fall into the furnace cavity? There appears to be some sealing foam where these wires go down into the hole inside the fridge cavity. I was thinking I can just dig that out so the wires can just fall through the hole?
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Old 11-23-2021, 06:14 PM   #4
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If your sure that the furnace wires go up to the fridge then you could cut them there. Only problem will be fishing them back up. And we use butt connectors.
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Old 11-23-2021, 06:23 PM   #5
mikec557
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I have the same TT and looked at that wiring long enough ago that I do not have a clear memory. But you're right, some of those wires are accessible from the back (outside) fridge area. But I think there's more access from the outside "kitchen" compartment. Take out the little fridge. The back wall and/or the right side wall come out with just a couple screws. There might be more accessibility going through there.

By the way, when you replace the oem spray foam, use closed cell foam. You shouldn't get a water spray in the outside fridge area, but just in case you do, use closed cell.
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Old 11-23-2021, 07:41 PM   #6
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Mark I don't know your exact situation but I can say that in years past with my adventures that the appliances seem to be placed without any thought of removal by an owner. I've always found I had to cut wires and put them back together with longer leads to allow future removal. I carry rolls of 12 & 14ga. wire in all colors used in the RV because it seems like the way it has to be done to "put it back together".
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Old 11-24-2021, 05:32 AM   #7
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Quote:
Originally Posted by chuckster57 View Post
If your sure that the furnace wires go up to the fridge then you could cut them there. Only problem will be fishing them back up. And we use butt connectors.
I agree, when I pulled my furnace to install my Cheap Heat, I added a terminal strip, just in case I needed to remove it again, which I did to remove a mouse.

Also tape a string or wire to the wires and you pull towards the furnace, once the furnace is fixed, that string or length of wire will make pulling the wires back through the hole.
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Old 11-24-2021, 06:34 AM   #8
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To me I read this as Chuck saying "splice the wires" to mean AFTER you cut them and remove the furnace. I think the OP. Understood doing this BEFORE removal.

Reach in, mark one of the blue wires. Easiest way I know is to take about 1/2" of painters tape and with one hand wrap it around the wire where you want to cut it. With a pair of good diagonal cutters cut the center of the tape. If your cutters arent great, use 2 peices of tape and cut inbetween them..

Then pull the furnace and make repairs. Splice wire long enough to reach in the emty cavity and reach outside to the furnace. Confirm the connections and re-install the furnace being careful not to pinch or otherwise compromise the wire. I like to use split wire loom covers and tape it closed at the ends and about every 6" or so with a wrap of electrical tape to keep the wires inside.
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Old 11-24-2021, 07:47 AM   #9
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Thanks all. Yes, Marshall, I understood what Chuckster meant. Even with the furnace out of the cavity, it will be hard to reach the remaining wires inside the cavity to add splices on to them. Not impossible, just hard

It was pretty cold overnight, but the furnace did start a couple times so we're not freezing I'll wait until I get back home and then work this out. I definitely need to enhance the wiring so I can get the unit out for inspection/repair as needed.
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Old 11-26-2021, 10:15 AM   #10
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I'm trying to determine the correct sail switch for my furnace. I'm pretty sure what I have is a Suburban DFMD35121, serial number 82998488, and based on what I can find, it looks like it should take Sail Switch part number 33082.

Can anyone confirm?

I got the furnace model number from the build sheet for my trailer - I haven't yet been able to pull it out far enough to read the label on it. That comes next. I would like to get the part ordered so it can be on it's way.

Thanks.
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Old 11-26-2021, 10:30 AM   #11
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If you have the model number then itís probably the righ part number. Are you sure thatís the issue?
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Old 11-26-2021, 11:10 AM   #12
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I'm not sure. I'm guessing based on what it's doing. I think it's either the sail switch or the control board. Here's what it's doing:

When we ask for heat, the blower starts and runs for about 10-30 seconds (sometimes long, sometimes short) and we hear no igniter clicking. Then it stops.

Sometimes, when we ask for heat, it works as expected. The blower runs for a few seconds and then we hear the igniter and the burner go - and we get heat.

It seemed that when it wouldn't light, we could turn it off (via the iN-Command system) for a minute or two, and then try it again and it might work. On our last night, however, it would not light at all - all night

I found I don't have all I need to cut/extend the wires, so I'll need to order some stuff- and I want to have the parts before I start cutting if possible.

By the way, I think the manufacturer's warranty on this furnace is only 2 years. Is that right? We're even beyond 3 years anyway, so I'm pretty sure there is no warranty.
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Old 11-26-2021, 11:20 AM   #13
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Manufacturers warranty is 2 years I believe. FWIW, if the sail switch is bad it will never try to light. Itís possible there may be some sawdust or other debris, but Iím not included to condemn the switch yet. If you do go with a replacement board get Dinasout brand.
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Old 11-26-2021, 11:33 AM   #14
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Thanks. I was going to order the switch in case I get in there and don't find anything obstructing the current switch. I've also heard that they can take a little oil to make them work better.

I'm just worried that I go through the effort to pull it out and find that the switch could use replacing and not have a spare.

Can I trust the build sheet provided with my trailer, or should I really pull the furnace out and inspect the label before ordering any replacement parts?

Do you think it's unwise to order a replacement sail switch without pulling the furnace first?
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Old 11-26-2021, 11:37 AM   #15
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By the way, I was assuming I would be able to test the unit outside of the trailer by connecting the wires and calling for heat. I realize there is no gas connected, but as the issue was that the igniter would not run, I would be able to hear that even without fuel.

Is there a connector/adapter which I can use to connect a standard propane tank to the furnace to allow for bench testing, which would regulate the fuel and allow for a connection to the furnace inlet? I've searched for this before and can't find what I think it needed.
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Old 11-26-2021, 05:02 PM   #16
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You would need a pigtail and regulator just like the camper has. Then it's just pipe fittings to go from the regulator out to the furnace in. The statement "I've also heard that they can take a little oil to make them work better.", personally I don’t use oil on anything where the issue is dust, dirt, or debris fouling the mechanical operation. Dust etc. Will stick to oil and create an issue. I use silicon spray lube for that type application, just my preference.
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Old 11-26-2021, 05:28 PM   #17
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Would this work? I'm not sure what fitting is needed on the hose end to connect to the furnace inlet: https://smile.amazon.com/Propane-Reg...dp/B07ZB7XNBB/
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Old 11-26-2021, 06:57 PM   #18
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Would a tool like this allow you to read the model number without pulling the furnace out further?

https://www.amazon.com/Telescoping-I...s%2C245&sr=8-5
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Old 11-26-2021, 07:42 PM   #19
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Originally Posted by MarkEHansen View Post
Would this work? I'm not sure what fitting is needed on the hose end to connect to the furnace inlet: https://smile.amazon.com/Propane-Reg...dp/B07ZB7XNBB/
Yes that would.
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